The present invention relates to a magnetic disk drive, and particularly to a magnetic disk drive having means for reducing disk deformation.
A flying head with a small air gap between the head and a disk are used in a magnetic disk drive. A high density recording requires an accurate positioning of the flying head. The position of the flying head can be divided into vertical and lateral components. The vertical position is the flying height or the air gap of the head. The lateral position is the position along the radius of the disk.
Preferably, the air gap is decreased because the decreased air gap enhances the electromagnetic transducing characteristic and allows the storage capacity to be increased. Products with an air gap of less than 0.1 .mu.m have recently been marketed.
However, the decreased air gap increases the probability of a head crash in which a head crashes against a disk and destroys information stored in the disk. A factor causing a head crash is disk deformation such as warpage and "wave" (e.g., buckling or waviness) illustrated in FIG. 1.
Referring to FIG. 1, warpage and wave are deformation radially and concentrically of the disk, respectively. More specifically, warpage of a disk is the difference in height between an innermost point A and an outermost point B on a radius. The disk deformation causes variation of the air gap. The variation of the air gap produces data read/write errors and may ultimately result in a head crash.
The extent of the disk deformation depends on a clamping mechanism that fixes the disks to a spindle hub. Referring to FIG. 2, a structure of a conventional magnetic disk is illustrated having four disks 100, and a spindle assembly 10 which comprises a spindle shaft 1 and a spindle hub 2. The spindle hub 2 is supported rotatably by the spindle shaft 1 via bearings 3A and 3B.
The spindle hub 2 has a cylindrical shape and has a flange 2A at its bottom end. The magnetic disks 100 and spacer rings 4 are alternately stacked on the flange 2A of the spindle hub 2 while the spindle hub 2 is fittedly inserted in the openings of the disks and spacer rings. A disk-like clamp ring 5 is placed on the top disk 100 and is attached to the top of the spindle hub 2 with screws (unreferenced). The disks 100 and spacer rings 4 are clamped between the clamp ring 5 and the flange 2A of the spindle hub 2. The disks 100 are affixed to the spindle hub 2 by pressure exerted by the screws.
The bottom surface of the clamp ring 5 and the top surface of the flange 2A of the spindle hub 2 that contact the disks 100 are flat so as to keep the disks 100 flat and parallel to one another.
However, this conventional clamping structure cannot reduce warpage of the disks 100 to less than 20 .mu.m because of an unavoidable irregular distribution of the clamping pressure.
Furthermore, in magnetic disk devices, the lateral positioning of the head must be precise to follow data tracks because track width has been generally decreased to increase track density. Lateral positioning accuracy is deteriorated by deformation of holder arms holding the heads. Arm deformation becomes critical when the track widths are decreased to less than 10 .mu.m. To complicate problems, the arms are becoming thinner so as to downsize the disk drive. This makes the holder arms prone to deformation.
Moreover, the deformation of the holder arms during manufacturing is unavoidable as stated below.
Specifically, the holder arms are formed by die-casting. However, since the arms are relatively thin, molten metal does not flow smoothly especially at the end portion of the die mold. This results in deformation of the arms and in blow holes being formed in the arms. Vibrations and loads during the processing also cause arm deformation.